Traditionally, absorbent articles such as diapers comprise an absorbent core with water-absorbent (cellulose) fibers and particles of superabsorbent polymer particle, also referred to as particles of absorbent gelling material or AGM, enclosed by a substrate material, or supported by a substrate material and then closed by a further material, e.g. such as a nonwoven.
Absorbent articles with so-called profiled absorbent cores have been developed, whereby certain regions of the article comprise more AGM than other regions. In such instances, accurate deposition of AGM is important to obtain the required profile. Furthermore, in the case of absorbent cores with only small amounts of, or no, cellulose fibers (having thus AGM particles as the only liquid storage material) accurate AGM distribution is highly important.
Various approaches have been proposed for obtaining absorbent cores with primarily AGM particles and for obtaining absorbent cores that have AGM particles in a specific profile or distribution, such as a predetermined pattern, MD-, CD- and/or thickness-profile. These approaches include indirect printing methods, whereby the AGM particles are taken up by a first surface, e.g. a drum surface, from a bulk storage of AGM particles—said drum surface having reservoirs, the number, size and position of which determines the amount and pattern of AGM granules taken up by the drum- and whereby the drum then rotates towards a substrate such as a nonwoven, to then release the AGM onto the substrate, for example carried by a moving surface, such as the surface of a further drum. For example, WO2006/014854 describes such a process.
The inventors found that such proposed indirect printing processes are in some instances difficult to run at high speed, for example at speeds of 800 ppm or more, or 1000 ppm or more (parts (absorbent structures) per minute), and/or when fine particulate material is used and/or when small (and large quantities of) reservoirs are used for printing. It has been found that at high speeds, the particulate material is not always accurately transferred onto the substrate material, resulting in for example dust creation, incorrect print of a specific profile etc. The inventors found that it may be beneficial to apply a strong vacuum to the substrate material to ensure better deposition of the particulate material onto the substrate.
However, the inventors found that with the prior art proposed apparatus it not always possible to maintain sufficient vacuum in a (cost) effective manner during the transfer of the substrate material with particulate material (for example to a further processing step) of the substrate with the AGM, in particular when running the apparatus at high speed. The inventors have now found an improved apparatus and process for depositing particulate material onto a substrate in an accurate manner and cost effective manner, even at high speed and/or even when fine particulate material is present, and/or even when very small quantities are transferred per surface area.